Gravity is a funny thing. It is strong enough to keep us from floating upwards, yet weak enough that it doesn’t crush us onto the surface of the Earth. Where ever we are on this planet, we all experience gravity in the same way. Although, apparently, we don’t, as this Potato Earth (BBC and Bad Astronomy) shows! Yellow shows areas of strong gravity, whereas blue indicates areas of weak gravity. This image is exaggerated approximately 10,000 times, but it still looks great. This shape is what is known as a geoid, and the image shows the “level” surface on an idealised world, or the ultimate sea level, if you will. If a ball were placed on this surface, it would not roll, as there is no “up” or “down” for it. It’s quite difficult to get your head around, but fascinating nonetheless.
The data comes from the European Space Agency’s GOCE satellite. GOCE (Gravity field and steady-state Ocean Circulation Explorer), which has been orbiting the Earth at an altitude of 170 miles (280km) for 2 years now, uses highly sensitive accelerometers to detect the minute tug of gravity on the satellite. Passing over an area of higher gravity causes the satellite to accelerate a bit, which is detected by the accelerometers, and results in the image seen above.
Really interesting stuff! I knew the Earth was a spheroid rather than a perfect sphere, but didn’t realise it was this lumpy! Now to visit southern India and see if I feel any lighter. Onwards!